We welcome the study by Slader et al¹ recently published in Thorax as the current state of our knowledge on breathing techniques for asthma is deplorable,² although such techniques are frequently used by physiotherapists when treating patients with asthma.³

Several aspects in this study may have influenced the results and need to be discussed.

First, the absence of evidence that upper body exercises, used as a comparator in this study, have an impact on lung function should not be confused with evidence that such an effect is absent. The two studies identified in the Cochrane review on breathing exercises for asthma,² that included forced vital capacity or forced expiratory volume in 1 s as an outcome, had only 8–12 patients in each group. If upper body exercises are in fact effective, the contrast between the two interventions may have been insufficient.

Second, we believe that more attention is needed for the hypothesis that the subjects recruited in this study were a special group. The patients were recruited using a database of volunteers and advertising in the lay press. In our view this may jeopardise the generalisability of the results to patients who consult a doctor for asthma.

Finally, the possibility that the two breathing routines provided a non-specific deferral strategy for reliever use needs further testing by, for example, comparing a breathing exercise with other (non-physical) deferral strategies.